1. Field of Application
The present invention relates to a vehicle-use communication apparatus to be employed in an intra-traffic communication system in which light emitted by a signal lamp of a traffic light apparatus is modulated to convey information that is transmitted to a vehicle, and whereby that vehicle can relay the information to a following vehicle.
2. Description of Related Art
As described for example in Japanese Patent first Publication No. 2004-13401, referred to in the following as reference document 1, a type of intra-traffic communication system is known in which a vehicle can receive information that is transmitted from a traffic light apparatus or from another vehicle, with the information conveyed as a signal that modulates the light emitted by a signal lamp of the traffic light apparatus or the light emitted by a tail lamp or headlight of the other vehicle. The receiving vehicle is equipped with a vehicle-use communication apparatus whereby the received information is demodulated and displayed on a display panel.
However with the apparatus of reference document 1, the signals used for communication between a traffic light apparatus and a vehicle are independent of the signals used for communication between vehicles. No specific method has been described whereby a vehicle that receives information transmitted as a light-modulated signal from a traffic light apparatus can transmit (relay) that signal to a following vehicle.
The information transmitted in that manner by a traffic light apparatus can for example express the indication condition of the signal lamps of that traffic light apparatus, or the time that will elapse until a changeover of the indication condition. However that information will be valid only for a vehicle that has almost reached the location of the traffic light apparatus. Alternatively stated, if the information is received by a vehicle that is approaching a preceding traffic light apparatus (i.e., which is at a location preceding that of the traffic light apparatus that is transmitting the information) then this can result in confusion to the driver of the latter vehicle.
Furthermore, in the case in which information relating to traffic accidents or traffic conditions or information relating to traffic restrictions is transmitted from a traffic light apparatus, the information may not necessarily be valid for vehicles which are located substantially distant from that traffic light apparatus.